Which of the following must every workers' comp insurance company operating in Indiana do?

Every workers' compensation insurance company operating in Indiana is required to become a member of the Indiana Insurance Guaranty Association. This membership is crucial because it provides a safety net for policyholders in the event that an insurance company becomes insolvent or goes out of business. The Indiana Insurance Guaranty Association ensures that claims can still be paid to claimants, thereby protecting workers and their rights to benefits under the workers' compensation system.

Membership in this association is designed to enhance the reliability of the workers' compensation insurance market, offering assurance to both employers and employees that they will have recourse in case of a financial failure of their insurer. It's a regulatory measure aimed at fostering stability in the insurance industry and ensuring that injured workers can still receive their benefits.

In contrast, the other options pertain to different functions or requirements that do not specifically pertain to workers' compensation insurance in Indiana. For instance, joining the Indiana Life and Health Insurance Guaranty Association or becoming a Lloyd's plan insurer is unrelated to the requirements for workers' compensation insurers specifically. Additionally, the requirement for a physical office size does not pertain to the operational aspects that are enforced to guarantee the availability of workers' compensation benefits.